1. Field of the Invention
The present invention relates to a cartridge life detecting system and in particular relates to a system for appropriately performing detection of life of a print cartridge, which is removably mounted for using on the body of an image formation apparatus such as a copying machine, facsimile apparatus or printer, before problems such as defect in image quality occur.
2. Discussion of the Related Art
Recently, various types of electrophotographic image formation apparatus employing a print cartridge in which an image formation member such as a photoreceptor is removably and exchangeably mounted on the body of the apparatus have been proposed, because the print cartridge requires repairing or exchange by reason of life expiration or the like. Therefore, checking, repairing or exchange of consumables such as an image formation member can be easily carried out.
In order to use plural types of such cartridges in exchange with each other, an image formation apparatus comprising a memory means in a cartridge, means for reading or writing of the memory means in the image formation apparatus, control means for operating information related to the life of the cartridge based on the contents read out of the memory means and image-forming operation and for writing information in the memory means has been proposed to the purpose of simply and accurately detecting and managing information related to the life of each cartridge or the like (Japanese Patent Application Unexamined Publications Nos. Sho. 63-212956 (1988) and Hei. 3-243978 (1991)).
In these apparatuses, contents of image formation operation as criterial information related to the life of cartridge, namely, the number of printed sheets or pixels, are set as a predetermined value corresponding to the life. It is determined whether the number of the printed sheets or pixels in the image formation practice exceeds the predetermined value. If it does not exceed the predetermined value, information is written in the memory means to continue image formation, and if it exceeds the predetermined value, exchange of the cartridge is recommended to the user.
When the number of the printed sheets is utilized as criterial information related to the life of the cartridge, counting the number of the printed sheets is carried out by calculating the number of ejected printed sheets or by presuming the number of the printed sheets based on the number of rotations of the image formation member and a predetermined rate.
If a print cartridge, integrally having an image formation member and a cleaner which collects toner remaining on the surface of the image formation member and stores the collected toner in the image formation member is used, the amount of toner stored in the image formation member is limited by the capacity of the toner storing component of the image formation member, and besides, the amount increases in proportion to the number of the printed sheets or the like, or varies by various factors. Therefore, there are some cases where toner storing component of the image formation member is filled with toner before the life of the cartridge expires.
In general, the amount of collected toner is almost equivalent to the amount given by subtracting the amount of toner transferred to the sheet from the amount of toner attached to the image formation member by development of an electrostatic latent image. However, the ratio of the attached toner amount to the transferred toner amount, namely, the transfer rate is not always constant. Ordinarily it varies within a range from 10 to 20% in accordance with variation of the toner charge amount (variation mainly caused by conditions such as frictional charging or circumstances). The amount of toner used for development also varies about 20% depending on the toner charge amount. Consequently, the real amount of collected toner varies more greatly under the above influences. In addition, the density of the image to be formed greatly affects the amount of attached toner in every printing process and the amount of collected toner.
For the above reason, in the case of the cartridge which stores the collected toner in the image formation member, a sensor detects that the toner storing component of the image formation member is filled with toner and notifies the user the time for exchanging the cartridge. To be more detail, it is detected that the driving torque of an auger exceeds a predetermined value by a torque limiter method utilizing increase of rotation load in the auger for carrying toner collected by the cleaner to the storing component of the image formation member, and the time for exchanging the cartridge is determined in accordance with the detection signal.
However, in the system for detecting the life of the cartridge such as described above, setting of the number of the printed sheets or pixels, or the amount of collected toner as criterial information related to the life of the cartridge is only based on ordinary mode of use (single-side printing for A4 size), and a special mode of use is not supposed. Therefore, defect in the image quality or apparatus contamination occurs before the life of the cartridge expires if the apparatus is used in a special way, for example, continuous use in a super density image mode, or continuous use in a double-side printing mode.
That is, owing to overuse or irregular use, a photoconductive film of a photoconductor as the image formation member is worn out and the charging potential of the worn out portion decreases, and therefore balance among conditions of developing potential contrast is lost, and fogging, which means producing high background density, the defect in the image quality occurs. Because of continuous use of the apparatus in the super density image mode, the amount of the collected toner abruptly increases, and accordingly, the storing component of the image formation member is filled with toner and then toner overflows the storing component, thus sometimes contaminating the inside of the apparatus.